Improvement of the Rpq parameter calculation

The standard deviation of the plateau height Rpq is a very important tribological parameter. However, the serious errors of its determination are possible when original procedure included in the ISO 13565-3 standard is used, because details from the valley region can be included in the plateau profile portion. Due to this error, the standard deviation of the plateau height can be overestimated. Two ways to improve the Rpq parameter calculations are proposed. The first of them depends on a modification of the procedure from the standard, while the second one recognises the starting and the finishing point of each plateau portion in a two-process profile.